last thursday and again today I experienced,out of know where, my heart started racing,followed by horrible sweating, hands shaking, dizziness,head spinning , and nausiness, lasting for about 30 minutes, then slowly began to calm down.  The same exact thing happened exactly one week ago today but today I lasted about 30 minutes compared to 20 minutes last week.  I have no known medical problems that I'm aware of, healthy my entire life and now this has occurred and I'm scared of what it may be.  Last week I thought maybe I needed to eat something or drink something cold , which seemed to help, but now the exact same happened today...out of know where..and I'm really concerned.  I'm 52 years of age, smoker, non-alcoholic drinker, and 5ft4 135 lbs.  Any idea what  might be the caused
                                                        
                                                     
                                                    
                                                        
                                                            
                                                            
                                                            
                                                                posted on
                                                            
                                                                Mon, 30 Sep 2013 
                                                            
                                                            
                                                            
                                                            
                                                                
                                                                    
                                                                    
                                                                    Mon, 30 Sep 2013
                                                                    
                                                                    
  Answered on 
                                                                 
                                                                
                                                                    
                                                                    
                                                                    Tue, 1 Oct 2013
                                                                    
                                                                    
  Last reviewed on